Seasonal and spatial variations of physicochemical parameters and heavy metals in surface water of interconnected Nigeria lagoons experiencing distinct anthropogenic disturbances – Nature

Executive Summary

A comparative assessment of Nigeria’s interconnected Lekki and Lagos coastal lagoons was conducted to evaluate the impact of varying anthropogenic activities on water quality and public health. This report analyzes physicochemical properties and heavy metal concentrations, framing the findings within the context of the United Nations Sustainable Development Goals (SDGs). The study reveals severe contamination in both lagoons, rendering the water unsuitable for drinking and posing significant ecological and human health risks. These findings directly challenge the achievement of SDG 6 (Clean Water and Sanitation), SDG 3 (Good Health and Well-being), and SDG 14 (Life Below Water). The primary sources of pollution were identified as industrial, agricultural, and urban activities, highlighting a critical need for improved practices in line with SDG 12 (Responsible Consumption and Production). Health risk assessments indicate that children are the most vulnerable group, facing potential non-carcinogenic and carcinogenic risks from exposure to Cadmium (Cd), Chromium (Cr), and Arsenic (As). The report concludes with recommendations for stringent monitoring, targeted remediation, and integrated coastal-zone management to protect these vital ecosystems and advance Nigeria’s progress towards the SDGs.

Introduction: Aligning with Sustainable Development Goals (SDGs)

The contamination of aquatic ecosystems by heavy metals is a global environmental crisis that directly impedes progress on several Sustainable Development Goals. The persistence and bio-accumulative nature of these pollutants threaten the fundamental principles of sustainability. This report investigates heavy metal pollution in Nigeria’s coastal lagoons, ecosystems vital for local livelihoods (SDG 8: Decent Work and Economic Growth) and biodiversity (SDG 14: Life Below Water).

The study’s objectives are intrinsically linked to the SDG framework:

• Assessing Water Quality for SDG 6: By examining physicochemical parameters and heavy metal levels, this study evaluates the suitability of lagoon water for drinking and other uses, providing critical data for monitoring progress towards Target 6.1 (universal and equitable access to safe and affordable drinking water).
• Evaluating Human Health Risks for SDG 3: The investigation into non-carcinogenic and carcinogenic health implications, particularly for vulnerable populations like children, directly addresses Target 3.9 (substantially reduce the number of deaths and illnesses from hazardous chemicals and air, water and soil pollution and contamination).
• Identifying Pollution Sources for SDG 12 and SDG 11: By tracing contaminants to industrial discharges, agricultural runoff, and urban waste, the study highlights unsustainable production patterns (SDG 12) and the environmental challenges facing urban communities (SDG 11: Sustainable Cities and Communities).
• Protecting Aquatic Ecosystems for SDG 14: The analysis of contamination indices and ecological risks provides a clear measure of the degradation of marine and coastal ecosystems, informing efforts under Target 14.1 (prevent and significantly reduce marine pollution of all kinds).

Study Context and Methodology

H3>Geographical Profile and SDG Relevance

The study was conducted in the interconnected Lekki and Lagos lagoons on the southwestern coast of Nigeria. These ecosystems are critical hubs for socioeconomic activities, including fisheries and transportation, which support local economies and livelihoods (SDG 8). However, they are under immense pressure from distinct anthropogenic sources:

• Lekki Lagoon: Primarily influenced by agricultural runoff, tourism, dredging, and municipal waste from coastal communities.
• Lagos Lagoon: Heavily impacted by industrial wastewater discharge, crude oil processing, shipping activities, and leaching from abandoned power plants, reflecting challenges in achieving sustainable industrialization and urban management (SDG 11, SDG 12).

The degradation of these lagoons threatens not only the aquatic biodiversity (SDG 14) but also the health and well-being of the communities that depend on them (SDG 3).

H3>Sampling and Analytical Protocol

To ensure robust data for SDG monitoring, a systematic approach was employed for sample collection and analysis.

1. Sample Collection: Surface water samples were collected over a 12-month period (December 2021 to November 2022) covering both wet and dry seasons from 15 strategic stations (9 in Lekki Lagoon, 6 in Lagos Lagoon).
2. Physicochemical Analysis: Parameters including pH, dissolved oxygen (DO), total suspended solids (TSS), electrical conductivity (EC), and total dissolved solids (TDS) were measured using standard methods.
3. Heavy Metal Analysis: Concentrations of eight heavy metals (As, Cd, Cr, Cu, Fe, Pb, Ni, and Zn) were quantified using an atomic absorption spectrophotometer (AAS) following USEPA digestion methods.
4. Quality Assurance: Rigorous quality control measures, including triplicate analyses, use of blank samples, and certified reference materials (CRM), were implemented to ensure data accuracy and reliability.

H3>Water Quality and Health Risk Assessment Frameworks

A multi-index approach was used to provide a comprehensive assessment of water quality and health risks, aligning with the need for evidence-based policymaking to achieve SDG 3 and SDG 6.

• Water Contamination Indices:
  • Single Pollution Index (Pi)
  • Contamination Degree (Cdeg)
  • Heavy Metal Evaluation Index (HMEI)
  • Heavy Metal Pollution Index (HPI)
• Water Quality Index (WQI): Used to assess the overall suitability of water for drinking purposes.
• Human Health Risk Assessment: A deterministic model was used to evaluate non-carcinogenic (Hazard Quotient, HQ; Hazard Index, HI) and carcinogenic (Target Cancer Risk, TCR) risks for both children and adults via ingestion and dermal contact pathways.

Analysis of Findings: Implications for Water Security and Ecosystem Health

H3>Physicochemical Water Quality Assessment

Most physicochemical parameters were within recommended limits, with the notable exception of Total Dissolved Solids (TDS) in Lekki Lagoon during the wet season, which exceeded safe levels for aquatic life and drinking water. The high TDS levels, linked to municipal waste and agricultural runoff, signal a direct threat to achieving SDG 6 and SDG 14. Furthermore, extremely high Chemical Oxygen Demand (COD) levels in Lagos Lagoon indicate severe organic pollution from industrial sources, undermining the goal of clean water bodies.

H3>Heavy Metal Contamination Profile

Heavy metal concentrations were significantly higher during the dry season and varied distinctly between the two lagoons, reflecting their different anthropogenic pressures. The average distribution trend was: Zn > Fe > Cu > Cr > Pb > Cd > As > Ni.

• Lekki Lagoon: Showed the highest concentrations of Cd, Pb, and As at stations influenced by agriculture, tourism, and dredging. This pollution compromises the safety of local food sources and water, impacting SDG 3 and SDG 14.
• Lagos Lagoon: Exhibited the highest levels of Cd, Cr, and Pb at stations dominated by industrial wastewater, crude oil processing, and shipping. This points to a failure in responsible industrial production (SDG 12).

Concentrations of most heavy metals, particularly Cd, Pb, Cr, and As, exceeded the permissible limits for drinking water in both lagoons, representing a severe public health concern and a major obstacle to achieving SDG 6.

H3>Source Apportionment and Anthropogenic Pressures

Multivariate analysis confirmed that the elevated heavy metal concentrations originate primarily from diverse anthropogenic activities rather than natural geological processes. This finding underscores the urgent need to address unsustainable practices that degrade the environment.

1. Lekki Lagoon Sources: Pollution is linked to agricultural runoff (agrochemicals), municipal waste disposal, and dredging activities.
2. Lagos Lagoon Sources: Pollution is driven by industrial effluent, oil processing and transport, shipping, and waste from manufacturing and power plants.

These findings highlight the direct conflict between current economic activities and the goals of sustainable urban development (SDG 11) and responsible production (SDG 12).

Integrated Risk Assessment and SDG Impact Analysis

H3>Water Contamination and Quality Indices

Integrated pollution indices revealed a dire situation, directly contradicting the aims of SDG 6.

• The Water Quality Index (WQI) scores for all sampling stations in both lagoons were above 100, classifying the water as “extremely unclean” and “unfit for usage” without treatment.
• The Heavy Metal Pollution Index (HPI) scores were also above the critical value of 100 at all sites, indicating extreme pollution levels.
• Approximately 90% of sampling stations showed moderate to extreme contamination levels, posing significant ecological risks and threatening the integrity of the aquatic ecosystem (SDG 14).

H3>Human Health Risk Evaluation (SDG 3)

The health risk assessment revealed alarming threats to human populations, particularly children, undermining the core principle of SDG 3 (Good Health and Well-being).

• Non-Carcinogenic Risk: The Hazard Index (HI) exceeded the safe limit (HI > 1) for children at approximately 33% of sites in Lekki Lagoon and 83% of sites in Lagos Lagoon. This indicates a high probability of adverse health effects from cumulative exposure to heavy metals.
• Carcinogenic Risk: The lifetime Target Cancer Risk (TCR) values for children at all sampling sites exceeded the acceptable threshold (1.0E-04). For adults, approximately 40% of sites posed a potential long-term cancer risk. The highest risks were associated with ingestion of Cd, Cr, and As.

These results demonstrate that water contamination in the lagoons poses a direct and severe threat to public health, with children being the most vulnerable demographic. This situation demands immediate intervention to protect community health and ensure progress towards Target 3.9.

Conclusion and Strategic Recommendations for SDG Achievement

H3>Summary of Key Findings

This study confirms that Nigeria’s Lekki and Lagos lagoons are highly contaminated with heavy metals from distinct anthropogenic sources, rendering the water unsafe for human consumption and posing severe risks to ecosystem health. Despite their hydrological connection, pollution profiles differ, with Lekki Lagoon impacted by agricultural and municipal sources and Lagos Lagoon by industrial activities. The contamination poses significant non-carcinogenic and carcinogenic health risks, especially to children, directly hindering the achievement of SDG 3, SDG 6, and SDG 14.

H3>Policy Recommendations for Sustainable Management

To address these challenges and align with the 2030 Agenda for Sustainable Development, the following strategic actions are recommended:

1. Enhance Monitoring and Enforcement (SDG 6, SDG 14): Establish stringent, long-term monitoring programs for land use and contaminant sources. Regulatory agencies must enforce discharge limits for industries and agricultural operations to prevent further pollution.
2. Implement Targeted Remediation (SDG 3, SDG 11): Deploy targeted remediation technologies at identified high-risk sites to mitigate existing contamination, protect community health, and begin restoring ecosystem functions.
3. Develop Integrated Coastal-Zone Management (SDG 17): Create and implement integrated management strategies that involve government agencies, industry stakeholders, and local communities. This fosters partnerships (SDG 17: Partnerships for the Goals) to balance economic development (SDG 8) with environmental protection and public health.
4. Promote Responsible Production (SDG 12): Incentivize and enforce the adoption of cleaner production technologies and sustainable agricultural practices to reduce pollutant loads at the source.

Analysis of Sustainable Development Goals in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

1. SDG 3: Good Health and Well-being
   • The article directly connects water pollution to human health. It conducts a “human health risks” assessment, identifying “potential non-cancer and carcinogenic health risks” from heavy metals like Cadmium (Cd), Chromium (Cr), and Arsenic (As). It specifically mentions that children are the “most vulnerable group,” linking the environmental issue to public health outcomes.
2. SDG 6: Clean Water and Sanitation
   • The central theme of the article is the degradation of water quality in Nigerian lagoons. It assesses “physicochemical properties and heavy metal levels” resulting from pollution and concludes that the water is “unsuitable for drinking.” The study’s recommendation for “stringent monitoring” and “targeted remediation” aligns with the goal of ensuring clean water.
3. SDG 11: Sustainable Cities and Communities
   • The article identifies “urban pollution,” “improper municipal waste management,” “urban development,” and “discharge of household sewage systems” as significant sources of contamination. This highlights the environmental impact of cities and communities on adjacent water bodies, connecting directly to the sustainability of urban areas.
4. SDG 12: Responsible Consumption and Production
   • The study explicitly names “industrial discharges” and “untreated effluents” from manufacturing industries as primary sources of heavy metal pollution. It details contaminants from petrochemicals, shipping operations, power plants, and textile warehouses, pointing to unsustainable production patterns that release hazardous chemicals into the environment.
5. SDG 14: Life Below Water
   • The research is set in coastal lagoon systems, which are vital marine ecosystems. The article notes that these lagoons are essential for “fisheries” and that the pollution poses “ecological risks for important ecosystem functions.” This directly addresses the impact of land-based pollution on marine and coastal environments.

2. What specific targets under those SDGs can be identified based on the article’s content?

1. Target 3.9: By 2030, substantially reduce the number of deaths and illnesses from hazardous chemicals and air, water and soil pollution and contamination.
   • The article’s detailed “health risk assessment” for carcinogenic and non-carcinogenic effects of heavy metals (As, Cd, Cr, Pb, Ni) directly addresses this target by quantifying the health threat posed by water contamination.
2. Target 6.3: By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally.
   • The study’s focus on pollution from “industrial discharges, agricultural runoff, and urban pollution” and the finding that industries “release untreated effluents that contain toxic metals” directly relates to the need to reduce the release of hazardous chemicals and untreated wastewater.
3. Target 6.6: By 2020, protect and restore water-related ecosystems, including mountains, forests, wetlands, rivers, aquifers and lakes.
   • The article assesses the degradation of “lagoon systems in Nigeria,” which are essential water-related ecosystems. Its conclusion about “potential uptake, accumulation, and ecological risks for important ecosystem functions” and the recommendation for “integrated coastal-zone management strategies to protect the lagoon ecosystems” align with this target.
4. Target 11.6: By 2030, reduce the adverse per capita environmental impact of cities, including by paying special attention to air quality and municipal and other waste management.
   • The identification of “urban pollution,” “municipal waste disposal,” and “landfilling” as primary sources of heavy metal contamination directly links the article’s findings to the need for better waste management in cities to reduce their environmental impact.
5. Target 12.4: By 2020, achieve the environmentally sound management of chemicals and all wastes throughout their life cycle… and significantly reduce their release to air, water and soil to minimize their adverse impacts on human health and the environment.
   • The article highlights pollution from industrial activities such as “crude oil processing, shipping activities,” and “industrial wastewater discharge,” which involve the release of heavy metals and chemicals. This directly relates to the need for sound management of industrial chemicals and waste.
6. Target 14.1: By 2025, prevent and significantly reduce marine pollution of all kinds, in particular from land-based activities, including marine debris and nutrient pollution.
   • The study investigates pollution in coastal lagoons originating from land-based sources like “industrial discharges, agricultural runoff, and urban pollution.” This is a direct examination of the problem described in Target 14.1.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

1. Concentrations of Pollutants:
   • The article provides specific quantitative measurements for various pollutants, which serve as direct indicators. These include:
     • Heavy Metal Concentrations: Measured in mg/L for Zinc (Zn), Iron (Fe), Copper (Cu), Chromium (Cr), Lead (Pb), Cadmium (Cd), Arsenic (As), and Nickel (Ni). These directly measure the level of hazardous chemical pollution (relevant to Targets 3.9, 6.3, 12.4, 14.1).
     • Physicochemical Parameters: Measured values for pH, dissolved oxygen (DO), total suspended solids (TSS), electrical conductivity (EC), and total dissolved solids (TDS). These are standard indicators of water quality (relevant to Target 6.3).
2. Composite Water Quality and Pollution Indices:
   • The study calculates several indices that synthesize complex data into a single score to assess water quality and pollution levels. These include:
     • Water Quality Index (WQI): Used to determine the overall suitability of water for drinking.
     • Heavy Metal Pollution Index (HPI) and other contamination indices (Pi, Cdeg, HMEI): Used to quantify the degree of heavy metal contamination. These indices serve as powerful indicators for tracking progress in reducing pollution (Target 6.3) and managing chemical waste (Target 12.4).
3. Health Risk Assessment Metrics:
   • The article uses specific models to quantify health risks, which can be used as indicators for Target 3.9. These include:
     • Hazard Index (HI): To estimate non-carcinogenic health risks. The article notes that HI values > 1 indicate a likelihood of adverse health effects.
     • Target Cancer Risk (TCR): To estimate the lifetime cancer risk from exposure to carcinogens. The article uses thresholds of 1×10⁻⁶ to 1×10⁻⁴ to classify the risk level.

4. Table of SDGs, Targets, and Indicators

Source: nature.com